Stoichiometric imbalances between detritus and detritivores are related to shifts in ecosystem functioning

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• 作者：Andr&#233 ; Frainer ; J&#233 ; r&#233 ; my Jabiol ; Mark O. Gessner ; Andreas Bruder ; Eric Chauvet and Brendan G. McKie
• 刊名：Oikos
• 出版年：2016
• 出版时间：June 2016
• 年：2016
• 卷：125
• 期：i6
• 页码：861-871
• 全文大小：865K
• ISSN：1600-0706

文摘

How are resource consumption and growth rates of litter-consuming detritivores affected by imbalances between consumer and litter C:N:P ratios? To address this question, we offered leaf litter as food to three aquatic detritivore species, which represent a gradient of increasing body N:P ratios: a crustacean, a caddisfly and a stonefly. The detritivores were placed in microcosms and submerged in a natural stream. Four contrasting leaf species were offered, both singly and in two-species mixtures, to obtain different levels of stoichiometric imbalance between the resources and their consumers. The results suggest that detritivore growth was constrained by N rather than C or P, even though 1) the N:P ratios of the consumers’ body tissue was relatively low and 2) microbial leaf conditioning during the experiment reduced the N:P imbalance between detritivores and leaf litter. This surprisingly consistent N limitation may be a consequence of cumulative N-demand arising from the production of N-rich chitin in the exoskeletons of all three consumer species, which is lost during regular moults, in addition to N-demand for silk production by the caddisfly. These N requirements are not commonly quantified in stoichiometric analyses of arthropod consumers. There was no evidence for compensatory feeding, but when offered mixed-species litter varying in C:N:P ratios, detritivores consumed more of the litter species showing the highest N:P and lowest C:N ratio, accelerating the mass loss of the preferred leaf species in the litter mixture. These results show that imbalances in consumer–resource stoichiometry can have contrasting effects on coupled processes, highlighting a challenge in developing a mechanistic understanding of the role of stoichiometry in regulating ecosystem processes such as leaf litter decomposition.